Re: [Qemu-devel] [PATCH 4/4] iothread: push gcontext earlier in the thread_fn

[Stefan Hajnoczi]

On Fri, Feb 22, 2019 at 02:57:24PM +0800, Peter Xu wrote:
> On Fri, Feb 22, 2019 at 07:37:02AM +0100, Marc-André Lureau wrote:
> > Hi
> > 
> > On Fri, Feb 22, 2019 at 4:14 AM Peter Xu <address@hidden> wrote:
> > >
> > > We were pushing the context until right before running the gmainloop.
> > > Now since we have everything unconditionally, we can move this
> > > earlier.
> > >
> > > One benefit is that now it's done even before init_done_sem, so as
> > > long as the iothread user calls iothread_create() and completes, we
> > > know that the thread stack is ready.
> > >
> > 
> > This will change the default context in the iothread, for code running
> > there. This may not be a good idea. Until now, only sources dispatched
> > from iothread_get_g_main_context() would have default context
> > associated to it.
> > 
> > I don't know if the current behaviour is intentional, but it has some
> > logic. With this change, you may create hidden races, by changing the
> > default context of sources to the iothread.
> 
> Yes I agree that the behavior will be changed in this patch that even
> if the iothread user does not use the gcontext they'll also have the
> context set.  I would think it should be ok because IMHO events hooked
> onto the aio context should not depend on the gcontext, but indeed I'd
> like to get some confirmation from others, especially the block layer.

I don't understand why Patch 4 is desirable.  The comment about
init_done_sem isn't clear to me but I also wondered the same thing as
Marc-André.

Can you explain why we should apply this patch?

Stefan

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